Sources said Ms. Perreault's termination was the result of her handling of a student's alleged threat to shoot up the sixth grade in December.

Rather than immediately report the threat to authorities, which state law mandates, she allegedly opted to try to handle the threat as an in-school matter, the sources said.

A number of parents have complained to the school committee about what they said are increased incidents of school violence this year.

The sources said Quincy lawyer Edward Doocey had been hired by the district to investigate Ms. Perreault's handling of the student's threat, and his findings were cause for her termination.

Mr. Doocey, who did not return a reporter's phone message, had also been asked to examine questions about Ms. Perreault's principal license, but the investigator's findings did not challenge her principal certification, the sources said.

At the time of the alleged threat, the public was on heightened alert about school violence. The Sandy Hook Elementary School shooting Dec. 14 in Newtown, Conn., resulted in the deaths of 20 students and six adults.

The alleged Southbridge threat was made by the same 16-year-old male student who had brought a pocketknife to school Dec. 18 and was charged with possession of a dangerous weapon in December, according to a source.

At the time, police described the incident as a merely a disagreement between two students. Authorities intervened, the students were checked and the knife was found.

Police downplayed the incident because the pocketknife was never taken out, exposed or used as a threat. However, police hadn't known about the threat to shoot up the sixth grade until the next day, sources said.

The other student involved in the disagreement allegedly told a teacher afterward the armed student had threatened to shoot up the sixth grade, and that teacher was said to have alerted Ms. Perreault, sources said.

Another school administrator, acting on Ms. Perreault's desire to handle the threat internally, allegedly told a parent of the student who'd been threatened not to talk to police about the threat. The parent was allegedly told the matter should be handled in-house, sources said.

The initial altercation was quickly handled because the school has a uniformed and armed resource officer in the building throughout the school day, then acting superintendent Terry L. Wiggin said at the time.

The appointment of Ms. Perreault was a lightening rod of controversy from the start.

Then Superintendent Eric D. Ely announced that Ms. Perreault had been promoted from district math director to principal of the new building for Grades 6-12 Aug. 2.

It was her first principal's position.

At the time of Ms. Perreault's appointment, she held only a license to be a principal in Grades 5-8. Though she had qualifications to be a licensed principal for high school students, she did not submit the paperwork until a week after the appointment.

The state would later verify she had the proper licenses to lead the building.

But various school officials said they found the timing pattern questionable.

Gregory Leach, a middle-high school assistant principal, has been serving as acting principal since Ms. Perreault was placed on leave.